The present invention relates generally to terrain conflict detectors for aircraft. More specifically, the present invention relates to stand alone terrain conflict detectors employing three dimensional (3D) representations of conflicts and avoidance vectors. Advantageously, methods for operating the stand alone terrain conflict detector are also disclosed.
An unacceptable number of aircraft crashes occur every year. In fact, this number has, on average, shown no significant sign of diminishing, in spite of advances in almost every aspect of aircraft technology. For example, most aircraft are now equipped with an inertial navigation system which allows them to determine their position after any interval from take-off. The inertial navigation system provides the components of the velocity and acceleration vectors of the aircraft as well as the components of the associated angles. It is possible to derive position data from this data; however, the position has a degree of uncertaintity associated with it. The position data from the inertial navigation system may be compared with position data provided by other radio navigational means, e.g., from a so-called Global Positioning System (GPS), which relies on satellites and which provides fairly precise position data with respect to latitude and longitude. Newer GPS systems can establish the aircraft position and altitude by triangulation using four or more satellites.
Even with these increasingly sophisticated systems providing position information, aircraft are still lost every year. Investigations into the causes of aircraft crash incidents frequently reveal that the aircraft was operating normally when the crash occurred, i.e., the cause of the crash incident could not be attributed to a system fault. In these types of incidents, often referred to as a Controlled Flights into Terrain (CFIT) accident or event, the cause is given as pilot error. However, although the pilot may have contributed to the event, had he been given sufficient warning that, for whatever reason, the aircraft was in imminent danger of crashing, evasive action could have been taken and ground contact avoided.
Systems which alert pilots to the fact that the flight path of their aircraft will intersect an obstacle or will make a close approach to such an obstacle are generally known. For example, U.S. Pat. No. 4,646,244 to Bateman discloses a system which utilizes Global Positioning Satellite (GPS) information to determine the aircraft's position. The position information is used to access stored data which can, in conjunction with the aircraft's position, provide an indication of the nature and location of the obstacles in the vicinity of the aircraft as well as the nature of the terrain. In the Bateman patent, the shapes and contours of the terrain are approximated by simple geometric shapes, e.g., boxes and triangles. When the flight path of the aircraft falls within a determined envelope, an aural warning is sounded. Additionally, U.S. Pat. No. 5,414,631 to Denoize. et al. discloses a system which also uses GPS signals and an alarm system to warn of approaching obstacles. The Denoize patent establishes a "floor" which in turn establishes a general minimum altitude that will provide obstacle clearance. The Denoize et al. patent uses the predicted flight path to warn pilots any time the aircraft is headed below this "floor." It will be appreciated that both of the above-described systems provide a warning of obstacles in the fligh path but provide no guidance regarding an escape maneuver.
Several recent systems which provide limited obstacle avoidance information are disclosed in U.S. Pat. No. 5,443,556 to Boyes et al. and U.S. Pat. No. 5,448,563 to Chazelle et al. These patents are discussed in detail immediately below.
The patent to Boyes et al. discloses aircraft terrain and obstacle avoidance systems which provide a warning signal whenever the aircraft is on a potentially hazardous course with respect to the terrain and obstacles which must be overflown. As illustrated in FIG. 1, the avoidance system proposed by Boyes et al., which is carried on-board an aircraft, includes:
1. an aircraft navigation system 11;
2. a computer system 15 having first, second, third and fourth computer sub-systems 17, 19, 21, respectively; and
3. A map data storage device 25.
It will be appreciated that the navigation system 11 develops outputs representative of aircraft geographical position in three dimensions, latitude, longitude, and altitude, respectively, of the aircraft, aircraft velocity V, again in three dimensions East (E), North (N), and Down (D) respectively, and aircraft attitude R, P, H, i.e., roll .phi., pitch .theta., and heading .psi. angles, respectively. The navigation system generates data representative of horizontal uncertainty PH (aircraft geographical position) and uncertainty PV (aircraft height). Aircraft altitude, (alt.) is derived by measurement.
The first computer sub-system 17 receives the horizontal uncertainty output PH from the navigation system 11 and develops outputs defining a notional navigation uncertainty grid pattern, as illustrated in FIG. 2. The second computer sub-system 19, upon receipt of outputs of aircraft present velocity, attitude, and geographical position from the navigation system 11, computes aircraft acceleration using the velocity input and develops outputs representative of the forward displacement of a reference point RP along the aircraft present flight path FP relative to aircraft present position CP. The third computer sub-system 21 receives the outputs of the second computer sub-system 19 and the output of the first computing sub-system 17, and develops, for each of several positions along the aircraft flight path, an output representing a multiplicity of sets of hypothetical pull-up trajectories. The output developed by the third computer sub-system 21 is applied to the fourth computer sub-system 23, which is also connected to the map data storage device 25. The fourth computer sub-system 23 additionally receives, from the navigation system 11, the output representative of aircraft height uncertainty PV.
The fourth computing sub-system 23 is operable, in the event that a predetermined relationship is detected between terrain and obstacle digital map data derived from the map data storage device 25 and the co-ordinates of any point along any notional trajectory in any of the multiplicity of trajectory sets, allowing for uncertainties in trajectory height measurement, to develop a warning signal at an output O/P. The predetermined relationship detected is that the aircraft height for any point along a trajectory, allowing for uncertainty, is equal to or less than the height for the terrain location corresponding to that point which is stored in the storage device 25. Thus, a warning signal is produced if the terrain area, i.e. search area, defined by the multiplicity of trajectory sets includes a point which is of greater height than the aircraft would have at the trajectory point corresponding to that search area point. It will be appreciated that since the trajectory sets relate to a reference point RP on the aircraft flight path forward of the current position CP of the aircraft, appropriate evasive action taken by the pilot in response to the warning signal will avoid terrain or obstacle contact by the aircraft.
In short, the system computes pull-up trajectories which the aircraft could carry out at a reference point (RP) on the current aircraft flight path (FP) forward of the aircraft current position (CP), taking into account uncertainties such as aircraft position, which trajectories collectively define a region moving ahead of the aircraft at a spacing ahead of the aircraft which is a function of aircraft velocity and acceleration and aircraft dynamic response to pilot demands and pilot reaction time, and therefore constitutes a region which the aircraft can imminently overfly. See FIG. 2. A warning signal is produced if any point on the trajectories has a predetermined relationship with data stored in a map data storage means containing height data relating to the region defined by the trajectories.
In contrast, U.S. Pat. No. 5,488,563 discloses a device for preventing collisions with the ground for an aircraft which includes a memory storing a data base representing a substantial part of the terrestrial globe in a grid configuration, wherein details are stored in greater detail, i.e., the grid is more precise, in the vicinity of an airport. Status indications are received representing the position of the aircraft in three dimensions, velocity and acceleration vectors of the aircraft, as well as control indications coming from the flight deck. In response to aircraft position, a temporary local map is transferred into a fast access memory. The map is used to establish an altitude envelope for the terrain in the vicinity of the aircraft. Anticollision processing is then performed; an alarm is sounded if the relation between a protection field and the altitude envelope meets a first condition which is defined at least partly by the control indications.
More specifically, the Chazelle et al. patent discloses a system illustrated in FIG. 3 which includes equipment 2 providing indications of the flight parameters. In particular, the equipment 2 generally includes, as illustrated in FIG. 4:
1. an inertial unit 20 or NU;
2. a radio navigational instrument 21, e.g., GPS system with its antenna; and
3. a radio altimeter 22 with its antenna.
The inertial unit 20 provides the components of the velocity vector (V) and the acceleration vector (A) of the aircraft, which may be used to derive characteristic angles such as the angle of incidence, yaw, slope, pitch, heading, bank, etc. For determining altitude, the inertial unit cooperates in the known way with a barometric altimeter (not shown).
The radio navigational instrument 21 provides uncorrected measurements of the latitude L1, longitude G1 and altitude Z1 (=Zgps) updated at a sequence p1 ranging from a few seconds to a few minutes. By integration of the velocity and acceleration vectors, the inertial unit 20 provides other measurements of the latitude L0, longitude G0 and altitude Zp (=Zbi). As illustrated in FIG. 4, a block 25 compares the two types of measurement and validates the values L1, G1, Z1, if they are consistent with L0, G0, Z0. The validated measurements L2, G2, Z2 are available at the time sequence p1. But they are upgraded from the inertial unit at a time sequence p2 of approximately one second. A block 28 extrapolates then the data between the last instant of measurement by the instrument 21 and the current instant. The radio altimeter 22 delivers the height above the ground, designated HRS.
A block 3, which contains a terrain file, is accessed using the values of L and G to thereby extract a local map, which and stored in a local memory. On the basis of this local map and the values of L, G, Z, and HRS, the block 4 performs anti-collision calculations, preferably accompanied by ground avoidance calculations. When a risk of collision is present, an alarm (51) is emitted. An order director 53 may also suggest an avoidance manoeuver which is conveyed to the flight deck. The local map may also be used for generating a synthetic image (60) with its visualization device 55.
The first two patents discussed above cannot provide the user with information which will assist him/her in avoiding the obstacle; these systems merely provide an audible warning whenever the projected flight path of the aircraft intersects the space occupied by the obstacle. More sophisticated systems, such as those described in the Boyes et al. and Chazelle et al. patents, generate escape vectors, which generally indicate the climb rate needed to achieve an altitude high enough to avoid the obstacle. Since these systems define airspace sections in terms of the highest point in a respective section, pilots relying on such systems would be forced to avoid, i.e., fly over, one or more airspace sections in order to avoid a single obstacle within those airspace sections even though the airspace sections could be safely navigated by the expedient of altering the aircraft's flight path by a few degrees. It will be appreciated that by dictating non-optimal solutions, pilots are forced to waste time and fuel to avoid obstacles.
Moreover, the systems discussed above have several features in common which make it difficult for them to gain wide acceptance in either commercial or private aviation communities. For example, several of the systems discussed above are programmed with both the performance capabilities of the aircraft and the reaction time of the pilots. Thus, many of the systems discussed above must be custom fit to the aircraft in which they are installed; the reaction time of the pilots is most probably programmed into these systems during pre-flight operations.
In addition, several of these systems, i.e., the system disclosed in U.S. Pat. No. 5,488,563, generate synthetic imagery, e.g., wire frame images based on the highest point in each map section. It will be appreciated that such representation do not convey significant intelligible information to the user of the system. In short, the collision warning is provided to the user, who cannot truly appreciate the danger given the displayed information.
Moreover, the systems discussed above are engineered to provide "just in time" warnings, since these systems take into account the performance capabilities of both the aircraft and the crew. These systems do not provide the flight crew with enough detailed information to assist the crew in assessing the danger and to assist the crew in arriving at an optimum solution to avoid a CFIT event.
Additionally, the systems disclosed by Boyes et al. and Chazelle et al. assume an ever-expanding region of uncertainty around the aircraft; this region of uncertainty requires the system to perform a myriad of complicated calculations in order to determine pull up and other avoidance trajectories i.e. flight paths, to compensate for uncertainty in the height and other location data. The primary warning signal in the systems by Boyes et al and Chazelle et al. is a "pull up" command.
What is needed is a stand alone terrain conflict detector which generates a terrain display that accurately depicts obstacles along a projected flight path using a variety of display images including three dimensional (3D) images. Moreover, what is needed in a stand alone terrain conflict detector which generates an optimal, i.e., minimal, conflict avoidance vector whereby a minimal flight path correction along the corresponding avoidance vector can be made to avoid the obstacle. Furthermore, a stand alone terrain conflict detector simple enough for any licensed pilot to operate with minimal training would be extremely desirable, particularly when color is made one indicia of conflicts detected by the stand alone terrain conflict detector. What would be even more desirable is a stand alone terrain conflict detector which could be used in developing a flight plan. Advantageously, the most desirable package for the stand alone terrain conflict detector would be a portable device which could be carried onto the aircraft by one of the flight crew.